Since this is a national (global, actually!) forum you'll have to do some leg work in your town. (yes there are national labs but I'm to anxious for my film to wait three days one way in shipping,)

I'd grab a yellow pages and look for photographers in your area that advertise table top or architectual photography, call and ask them where to go. Or find the local College photo department and ask where the students get their processing done. Some colleges have labs on campus and may accept outside work. Others have found a nearby lab to do it for them

Welll... no reason that I am aware of for B&W negatives other than the difficulty and expense of gathering up; film holders, three to seven deep tanks, a large format enlarger and lens to match it.

When you start working with process C41and E6 (not sure if these are the current versions) chemistry, the difficulty and expense increases quite a bit... not to mention the noxious fumes from bleaching agents.

I am currently working on upgrading my 35mm/6x6 darkroom to accomodate 4x5 B&W. Bear in mind that I can use the same paper trays, safe lights, tongs, timers, etc. I have over a hundred dollars invested so far in the upgrade buying only used equipment, and still have to acquire some deep tanks and possibly an enlarger lens.

Processing techniques vary a bit, but are basically the same as for other formats. Anyone who can process 35mm can process 4x5... though not everyone will. For day to day activities, I will probably elect to have much of my own stuff processed by a lab. Only when I start getting into contests again will I delve into darkness. You can't get anyone to use fiber-based paper and archivally process the prints any more.

I wouldn't be too anxious to go the "deep tank" route, unless you intend to process an awful lot of film. It doesn't take long to recognize that 3 1/2 gal. is a LOT of chemistry - especially when it starts deteriorating as soon as you mix it! I'm much happier just mixing up a half gallon [4x5 tank] or even a gallon [5x7 tank]. The stop and fixer lasts much longer than the dev. so it isn't a hardship to mix batches of dev. as needed.

Also, the hangers are cheaper, you can easily find substitutes for the old-time hard rubber tanks if you look [e.g. yankee tanks], and single hangers are easier to handle than the 4-ups. No substitute, however, if you're going to shoot a LOT of film, so you have a choice. I'd suggest working your way up. Maybe you won't find the need for the deep tanks.

I started with 3 1/2 gal. because I wanted to use gas burst. Even then, I quickly discovered it was much easier to scale everything down. I now use a 5x7 tank for dev. [provides room for a gas plenum] and 4x5 tanks for everything else. Good luck!

I decided from the start that my B&W would be processed myself (I'm a do-it my selfer).

I already had all the chemicals because I develop my own medium format. Look at Adorama.com and get the HP-Combi plan 4X5 tank. It'll hold six sheets or 12 B&W back to back. It comes with a reversible holder so you can use plates as well, if you want to. Made of plastic so there is reduced chance of scratching the sheets.

It also comes with load assistors, and a funnel. It has two fill spouts(one top and bottom) and you can day process it because of the rubber lid. This is a better unit than the Yankee because the rubber lid permits inverting the tank. Price? about $50.00. Worth it? YES!!! You'll start saving money right away.

One other note: It is an adjustable holder so you can also do smaller formats (4x5 is the largest however).

Use your saved money to pay for processed slide, which is a whole 'nother ball game.

I rec'd a graflarger off of ebay for $120 complete with neg carrier and now I am equipped to do large processing and printing with a total cost of about $200 less chemicals.

I'd also look at Yankee agitanks. These are similar to HP combi, but hold 12 sheets. they are invertable like the combi but are easier to use than FR tanks. They also fill and dump chemicals faster than combi.

In both cases I would still fill the tank with developer first then put the film in, cover and turn the lights on. This prevents devloper from pouring over parts of the film and reduces streaking and uneven development.

Before I moved into 5x7 and 8x10 I used three of the yankees and processed in daylight and switched tanks in the dark. These have been going cheap on ebay lately. I think these are much easier to use than hangers. Total volume is more than a combi but at less than 60oz still small enough to use one shot developers.

_________________"In order to invent, you need a good imagination and a lot of junk" Thomas Edison